Ion pumps are used in a variety of scientific and technological applications to create high and ultra high levels of vacuum (i.e., very low absolute pressures) within a vacuum chamber. For example, ion pumps are often used with scanning electron microscopes (SEM), mass spectrometers, Auger electron microprobes, particle accelerators, and a variety of particle beam devices. They are also used in vacuum tube processing, development and production of semiconductor devices, and space simulation. A number of other instruments and apparatuses use ion pumps.
The vacuum level in a vacuum chamber can be characterized by the gas pressure within the chamber. Whereas atmospheric pressure is about 1×103 mbar (750 torr), an application requiring a high or ultra high vacuum level, such as those discussed above, may require a vacuum level on the order of 1×10−5 mbar (7.5×10−6 torr) down to 1×10−11 mbar (7.5×10−12 torr) or even lower. For comparison, the pressure in interstellar deep space is on the order of 10−16 torr. Pressures below 1×10−5 mbar can be called high vacuum, and pressures below 1×10−8 mbar can be called ultra high vacuum.
A vacuum can be created within a chamber with a piston-style pump, a turbo-molecular pump, or other mechanical pump. However, the vacuum level associated with a piston-style mechanical pump is inadequate for applications that require very high or ultra high vacuum pressures. A turbo-molecular pump can produce ultra high levels of vacuum but may exhibit detrimental effects such as mechanical vibration or contamination from pump fluids. Accordingly, mechanical pumps are incapable of producing clean, vibration free high or ultra high vacuum levels required in many applications.
Ion pumps are known in the art for generating high or ultra high vacuum levels within a chamber. Ion pumps do not mechanically pump gases out of a chamber, but rather function by converting gases within a chamber to solids that are then deposited on surfaces within the ion pump, as well as through physisorption of gases (particularly noble gases) on surfaces within the ion pump. According to the law of ideal gasses, the pressure inside of a fixed volume at a fixed temperature is proportionate to the number of gas molecules present. Therefore, by capturing gas molecules and converting or binding them to solids, the gas pressure inside the chamber is reduced.
Ion pumps constructed in a conventional manner have performed successfully in a number of applications. However, it has been found in certain applications that a conventional ion pump does not perform as well as is desired. Improved ion pumps are needed.